When drilling for oil or gas, accurately and precisely tracking the position of the borehole can be vitally important. For example, a directional driller may need to orient the borehole such that it either avoids or intersects one or more existing boreholes. Knowing the position of the borehole also allows the borehole to be drilled at an angle such that oil recovery from a reservoir can be increased by ensuring that the area of intersection between the borehole and the reservoir is relatively high. Furthermore, knowing the position of the borehole may be important to ensure that drilling does not occur in a prohibited area, such as an area in which only a competitor has rights to drill. Even when the borehole is intended to extend vertically, tracking the position of the borehole can be important to ensure that the borehole is, in fact, being drilled vertically.
To track borehole position, a measurement-while-drilling (“MWD”) tool can be used. A MWD tool contains measurement instruments that are located within a drill string and typically near a drill bit. The MWD tool typically measures a variety of parameters relevant in directional drilling, such as:                drill string inclination;        drill string azimuth;        toolface;        gamma rays;        resistivity of surrounding rock; and        various diagnostic information (temperature, battery status, dip angle, total magnetic field strength, and total gravitational strength).        
The MWD tool communicates measured parameters by sending a signal to the surface using any one of a variety of known transmission techniques, such as mud pulse telemetry, electromagnetic telemetry, and wired pipe. The transmitted information is then used by any one or more of the directional driller, a geologist, and a MWD technician to drill the borehole according to a predetermined trajectory.
The signal the MWD tool transmits can be encoded according to a cipher that is proprietary to the MWD tool manufacturer. Consequently, in order to decode the signal, a decoder that the MWD tool manufacturer provides is required. In other words, a one-to-one dependence typically exists between the MWD tool and the decoder used to decode signals that the MWD tool transmits. This setup can be cumbersome when a user wants to use a single piece of hardware to decode signals sent from a variety of different MWD tools.
Accordingly, there exists a need for at least one of a method and apparatus for decoding a signal sent from a MWD tool that improves on the prior art.